Typical motor graders have all-wheel drive capability with one or more front motors for driving the front wheels and a separate rear transmission for driving the rear wheels. The transmission and the clutch for the front motors typically include a free-wheel capability, meaning that the front wheels are allowed to rotate at a speed faster than they are being driven by the front motors. Therefore, when the rear motor drives faster than the front motors, the front wheels roll freely and will not drag. This is important because the front wheels provide steering capability to the motor grader, and if the front wheels drag, the motor grader's ability to turn is limited.
Although the front and rear wheels typically rotate at the same speed during straight ahead travel, when turning, one or both of the front wheels are required to rotate faster than the rear wheels. In fact, a full turning motor grader may have front wheel speeds that are up to 50% faster than the rear wheel speeds. When this occurs, the front wheels may rotate faster than the driving front motors, thereby causing free-wheeling. Whenever the front wheels are free-wheeling, they are not providing traction into the turn, which can reduce the steerability of the motor grader, and increase the turning radius. Motor graders having a tandem arrangement of rear wheel sets resist turning more than those with a single rear wheel set. Accordingly, the problems associated with free-wheeling on a motor grader with tandem rear wheel sets may be even greater.
One system for driving front wheels on a motor grader is disclosed in U.S. patent application Publication No. US 2002/0027025 (the '025 publication) to Kobayashi et al. The '025 publication discloses a system for rotating the front wheels faster than the rear wheels based on the turning radius and the revolution number of the rear wheels. The system measures a front wheel steering angle and an articulation angle, and controls the speed of the front wheels based on the measured factors. However, the '025 publication discloses that a single pump drives both front wheels. Further, the '025 publication discloses an open loop system that cannot compensate one wheel independent of the other to increase traction in a turn. Such a system may result in a loss of traction from at least one front wheel during a turn.
This disclosure is directed to a system and method for independently controlling the front wheel speeds of a work machine by independently adjusting the desired front wheel speeds based on a steering angle or a combination of steering and articulation angles, for example.